The present invention relates to an article comprising a multilayer film suitable for packaging end use, especially a multilayer film suitable for use in the packaging of relatively hard, granular bulk products, such as dry pet food. The multilayer film can be a laminate of two components wherein the first component comprises at least three film layers, and a second component has an oxygen barrier layer. The exposed first component surface is heat-sealable to both itself (end sealable) and the second component surface (lap sealable) while the exposed second component surface is heat-sealable to itself (gusset seal) as well to first component (lap sealable). The article preferably comprises a heat seal of the film to itself or another film. The external surface of the article comprises a film layer which can be free of anti-block and slip additives to improve stackability of the articles. The present invention also relates to packaged products in which the package comprises the article of the invention.
For some time various products have been packaged in packages which comprise paper alone or paper in combination with a thermoplastic film. Such packaging has typically included a plurality of paper layers, with a relatively thin, flexible plastic film adhered to the inside paper layer, the film serving as a moisture and grease barrier. The paper provides the package with an exterior surface which is highly printable, as well as a stiffness which provides the packaging article, which is, for example, a gusseted bag, with an ability to be self-supporting and to provide the package with overall aesthetic qualities which consumers perceive as being desirable. Such paper packaging has been used in a variety of applications, particularly gusseted bags which are used in the packaging of dry granular material such as pet food, livestock feed, sugar, coffee, cookies, cereals, baking products such as cake mixes, crackers, chips, powdered milk, charcoal, cement, fertilizer, lime, pesticides, etc. The packaging can also be used to package cheese, in grated, ground, and/or block form.
More recently, paper-free plastic film packaging materials have been used for the packaging of a such products as pet food, etc. In order to obtain a desirable performance level, i.e., in terms of impact strength and toughness, such packaging films have contained relatively large quantities of polymers which are recognized.for their toughness and impact resistance, such as polyamide, polyester, and polyacrylonitrile. However, these polymers are also relatively expensive. It would be desirable if a comparably tough, impact-resistant package could be made from less expensive polymers. Moreover, it would also be desirable to provide packaging which provides a high O2-barrier layer to increase the shelf-life of the product. In addition, in such plastic packaging, particularly in the packaging of hard, granular bulk products such as dry pet food, it has-been found that xe2x80x9cdimplesxe2x80x9d tend to form in the plastic, thereby creating a rough, dimpled appearance in the outside of the package. It would be desirable to provide packaging which avoids this xe2x80x9cdimplingxe2x80x9d effect. Finally, it would be desirable to provide such packaging which is also relatively stiff, e.g., capable of providing a self-supporting gusseted bag.
In the case of the packaging of food in paper packaging, particularly pet food, it has heretofore been desirable to mix antioxidant into the food product, otherwise the food tends to lose metabolizable energy, exhibit decreased acceptability, including undesirable odors and flavors, protein degradation, and the development of health hazards in .the consuming animal. Thus, without antioxidant present, food packaged in paper packaging exhibits reduced shelf life and/or reduced product quality. It would be desirable to provide a type of packaging which requires less antioxidant, or even no antioxidant, to be mixed with a food product within the package, without the detrimental effects associated with the oxidation of the food product. In this manner, the expense of providing the antioxidant as well as the mixing of the antioxidant with the food product, are both reduced or avoided, while maintaining a good shelf life for the packaged food product.
U.S. Pat. No. 5,846,620 to Compton discloses a high strength bag which is made from a self-sealing heat-shrinkable film comprising at least three layers, e.g., LLDPE/EVA/LLDPE. U.S. Pat. Nos. 4,765,857 and 4,755,403 to Ferguson also disclose such multilayer films.
PCT Application WO98/22282, published May 28, 1998 discloses tough and impact resistant bags which are substitutes for paper packaging while being made for the most part from less expensive polymers. The bags are made by laminating a three film layer first component (inside bag surface) to a second component (outside bag surface) containing at least a fourth film layer, e.g., a non-self-sealing blown monolayer film such as high density polyethylene, as substitutes for paper packaging. However, such bags have been difficult to form seals with second component surfaces, requiring offset printing and laminating steps to create an edge lip of first component which extends beyond the second component to permit better lap sealing by allowing first component overlap of a first component surface. Although this construction provides for both inside/outside and outside/outside seals, the extra steps result in added manufacturing expense. Moreover, while large bags require good stackability on a pallet, the second component film employed requires slip and antiblock additives for processing, resulting in a slippery outer surface of the bag, hindering stackability. Moreover, embodiments which employ heat-shrinkable, unblown or solid state oriented second component equivalent barrier film (Examples 1 to 4) exhibit reduced interply adhesion which results in weak gusset seal in the bags. Finally, difficulty in maintaining repeat length of the bag arises when temperatures encountered during processing,. e.g., during ink drying and laminating adhesive drying, result in unintended shrinkage.
Accordingly, it would be useful to provide plastic bags which are sufficiently inexpensive to compete with paper-containing packages while providing a high quality appearance and feel to the consumer. Such articles would comprise a multilayer film having excellent optics and improved ink adhesion for appearance, high coefficient of friction (COF) on its outer surface for stackability of packages made with such film, strong interply adhesion to promote both gusset sealing and lap sealing for bag strength, as well as reduced shrinking tendency at processing temperatures of 110xc2x0 to 150xc2x0 F. to maintain repeat length during manufacture.
The present invention is directed to a multilayer film as well as an article which is suitable for packaging end-use and which comprises a multilayer film. The majority of the multilayer film is made from relatively inexpensive polymers. Nevertheless, it has been found that the multilayer film can be provided with toughness and impact resistance characteristics which are adequate for the packaging of various products, including dry pet food. Moreover, it has been found that the multilayer film can be provided with toughness and impact resistance characteristics which are comparable to, or even superior to, plastic packaging materials which comprising higher amounts of more expensive polymers such as nylon, polyester, and polyacrylonitrile.
In addition, the multilayer film in the article of the present invention comprises an O2-barrier layer which increases the shelf life of, for example, a packaged food product therein. The presence of the O2-barrier layer reduces or eliminates the need to add antioxidants, etc. to a food product, such as pet food, to prevent the oxidative rancidity, off-flavors, and off-odors of the packaged food product. The multilayer film also can be provided with a stiffness which, if the multilayer film is converted to a gusseted bag, provides a self-supporting packaged product. Preferably, the multilayer film is resistant to shrinkage at processing temperatures of 110xc2x0 to 150xc2x0 F. to maintain repeat length during manufacture. The multilayer film can also be provided with: (a) high gloss, to provide a packaged product having enhanced aesthetic appeal, (b) good resistance to tear propagation, (c) printing on the surface of the film, and/or printing which is trapped between the layers of the film, and (d) high impact strength.
As a first aspect, the present invention is directed to a two-component laminated multilayer film which comprises at least 5 layers. The two-component laminated multilayer film comprises:
I. a first component comprising:
(A) an outer first film layer comprising ethylene/alpha-olefin copolymer;
(B) an optional second film layer comprising at least one member selected from the group consisting of ethylene/unsaturated ester copolymer, anhydride-modified ethylene/alpha-olefin copolymer, anhydride-modified ethylene/ester copolymer, acid-modified ethylene/alpha-olefin copolymer, and acid-modified ethylene/acid copolymer;
(C) an optional third film layer comprising ethylene/alpha-olefin copolymer; and
II. a non heat-shrinkable second component laminated to said first component, said second component comprising:
(D) an outer fourth film layer which comprises at least one member selected from the group consisting of ethylene/alpha-olefin copolymer and ethylene/unsaturated ester copolymer;
(E) a fifth film layer which serves as an O2-barrier layer, the fifth film layer being between the third film layer and the fourth film layer, the fifth film layer comprising at least one member selected from the group consisting of PVDC, EVOH, polyalkylene carbonate, polyacrylonitrile, polyamide, and polyester;
(F) a sixth film layer which is between the fourth film layer and the fifth film layer, the sixth film layer serving as a first tie layer and comprising at least one member selected from the group consisting of ethylene/unsaturated ester copolymer, anhydride-modified ethylene/alpha-olefin copolymer, anhydride-modified ethylene/ester copolymer, acid-modified ethylene/alpha-olefin copolymer, and acid-modified ethylene/acid copolymer; and
(G) a seventh film layer which is between the third film layer and the fifth film layer, the seventh film layer serving as a second tie layer and comprising at least one member selected from the group consisting of ethylene/unsaturated ester copolymer, anhydride-modified ethylene/alpha-olefin copolymer, anhydride-modified ethylene/ester copolymer, acid-modified ethylene/alpha-olefin copolymer, and acid-modified ethylene/acid copolymer;
wherein the multilayer film is sealable to at least one member selected from the group consisting of itself and another film, and said outer fourth film layer is heat sealable to itself as well as to said outer first film layer.
By xe2x80x9cnon heat-shrinkable second componentxe2x80x9d is meant that the second component, measured independently of the laminate, has a total free shrink (i.e., L+T), of less than 5 percent at 180xc2x0 F., with the quantitative determination being carried out according to ASTM D 2732, hereby incorporated in its entirety, by reference thereto. Conversely, the term xe2x80x9cheat-shrinkablexe2x80x9d as used herein means a total free shrink of at least 5 percent at 180xc2x0 F., preferably at least 15 percent at 180xc2x0 F., with the quantitative determination being carried out according to ASTM D 2732, hereby incorporated, in its entirety, by reference thereto. The multilayer film, i.e., the two component laminate of the present invention, can be heat-shrinkable. If heat-shrinkable, the multilayer two component laminate film preferably has a total free shrink (i.e., machine direction plus transverse direction or L+T), of at least 5 to 50 percent, at 180xc2x0 F., more preferably, a total free shrink of from about 10 to 30 percent at 180xc2x0 F., more preferably, a total free shrink of from about 10 to 20 percent at 180xc2x0 F.
Preferably, the first component is heat-shrinkable and heat sealable to itself, the second component comprises a non heat-shrinkable film oriented at about or above its melt temperature, e.g., at about 440xc2x0 F. The multilayer film can have a total thickness of at least 2 mils, an impact strength of at least about 3.0 ft-lbs (preferably, at least 4 ft-lbs, more preferably, at least 5 ft-lbs, more preferably, at least 6 ft-lbs) a tensile strength at break of at least 8,000 pounds per square inch (preferably, at least 9,000, more preferably, at least 10,000, more preferably, at least 11,000), an elongation at break of less than 300% (preferably, less than 250, more preferably, less than 200), a tear propagation of at least 50 grams, preferably from 80 to 800 grams, more preferably from 100 to 400 grams, a tensile modulus of at least 45,000 psi (preferably, from 45,000 to 250,000, more preferably, from about 45,000 to 100,000), total free shrink at 150xc2x0 F. of less than 10%, total free shrink at 200xc2x0 F. of less than 30%, elastic recovery of at least 80%, preferably at least 85%, more preferably at least 88%, when subjected to stress or extension of about 10%, and having a first component to second component seal-strength of at least 4 pounds/inch at a seal time of 1.5 seconds on a VERTROD(copyright) impulse heat sealing machine with wires top and bottom, 70% seal power, total dwell time 5.0 seconds, and room temperature cooling.
Structures for the multilayer film of the present invention are as follows:
First Layer: seal layer and inside layer (e.g., inside layer of sealed article), preferably ethylene/alpha-olefin copolymer;
Second Layer: inner layer preferably comprising at least one member selected from the group consisting of ethylene/unsaturated ester copolymer (especially ethylene/vinyl acetate copolymer) and other suitable for self welding, such as ethylene/methyl acrylate copolymer, ethylene/butyl acrylate, ethylene/methacrylic acid copolymer, etc;
Third Layer: inner layer preferably comprising ethylene/alpha-olefin copolymer;
Fourth Layer: outside layer preferably comprising ethylene/alpha-olefin copolymer;
Fifth Layer: inner oxygen barrier layer comprising at least one member selected from the group consisting of ethylene/vinyl alcohol copolymer (EVOH), vinylidene chloride copolymer, polyamide, polyester, polyacrylonitirile, polyalkylene carbonate, etc.;
Sixth Layer: a first tie layer preferably comprising at least one member selected from the group consisting of ethylene/unsaturated ester copolymer (especially ethylene/vinyl acetate copolymer and modified ethylene/unsaturated ester copolymers), anhydride-modified ethylene/alpha-olefin copolymer, etc., the sixth layer being between the fourth layer and the fifth layer;
Seventh Layer: a second tie layer preferably comprising at least one member selected from the group consisting of ethylene/unsaturated ester copolymer (especially ethylene/vinyl acetate copolymer and modified ethylene/unsaturated ester copolymers), anhydride-modified ethylene/alpha-olefin copolymer, the seventh layer being between the third layer and the fifth layer;
Eighth Layer: a layer preferably comprising at least one member selected from the group consisting of ethylene/alpha-olefin copolymer (e.g., low density polyethylene) ethylene/unsaturated ester copolymer (e.g., ethylene/vinyl acetate copolymer), the eighth layer being between the third and seventh layers, the eighth layer contacting the laminating adhesive between the first component and the second component;
Ninth Layer: a laminating adhesive layer, preferably polyurethane based, the ninth layer being between the third and eighth layers;
Tenth Layer: an oxygen barrier layer (preferably a supplemental layer) preferably comprising polyamide, the tenth layer being between the fifth and sixth layers;
Eleventh Layer: an oxygen barrier layer (preferably a supplemental layer) preferably comprising polyamide, the eleventh layer being between the fifth layer and the seventh layer.
Thus, a preferred structure for the multilayer film of the present invention is as follows: 1/2/3/9/8/7/11/5/10/6/4. Another preferred structure is 1/2/3/9/8/7/5/6/4; yet another is 1/2/3/9/8/7/11/10/6/4; yet another is 1/2/3/9/8/7/10/6/4; yet another is 1/9/8/7/11/5/10/6/4; yet another is 1/9/8/7/5/6/4; yet another is 1/9/8/7/10/6/4. Typically, layers 1, 2, and 3 make up the first component, while layers 4, 5, 6, 7, 8, 10, and 11 make up the second component, with layer 9 making up the laminating adhesive used to laminate the first component to the second component. Clearly, in the above-described multilayer films, some embodiments do not utilize all of the listed layers.
In a more preferred embodiment, the fifth film layer comprises EVOH, the tenth film layer comprises polyamide and the eleventh film layer comprises polyamide. Polyamides, such as nylon, e.g., nylon-6, can provide additional stiffness giving additional structural support as well as providing an oxygen barrier multilayer film which is less likely to undesirably stretch or misregister during processing. The combination of EVOH and polyamide can also contribute to improved tearability of the resulting product.
Preferably, the second film layer comprises ethylene/unsaturated ester copolymer, the third film layer comprises ethylene/alpha olefin copolymer, the fourth film layer comprises ethylene/alpha-olefin copolymer, the fifth film layer comprises EVOH, the sixth film layer comprises ethylene/unsaturated ester copolymer, the seventh film layer comprises ethylene/unsaturated ester copolymer, the eighth film layer comprises ethylene/alpha-olefin copolymer, the ninth film layer comprises polyurethane adhesive, the tenth film layer comprises polyamide and the eleventh film layer comprises polyamide.
Even more preferably, the first film layer comprises at least one member selected from the group consisting of LLDPE and LDPE, said second film layer comprises EVA, said third film layer comprises at least one member selected from the group consisting of LLDPE and LDPE, said fourth film layer comprises at least one member selected from the group consisting of LLDPE and LDPE, said sixth film layer comprises EVA, said seventh film layer.comprises EVA, said eighth film layer comprises at least one member selected from the group consisting of LLDPE and LDPE ethylene/alpha-olefin copolymer, said ninth film layer comprises polyurethane adhesive, said tenth film layer comprises nylon and said eleventh film layer comprises nylon.
The multilayer film of the invention can have a first component which comprises a downward cast solid state oriented film biaxially oriented to a total orientation (L+T) of from about 5xc3x97 to 25xc3x97, preferably 6xc3x97 to 20xc3x97, more preferably 9xc3x97 to 16xc3x97, at a temperature of from about 200xc2x0 to 280xc2x0 F. The second component can comprise a non heat-shrinkable melt-oriented upwardly blown film, i.e., a film which is oriented at or near its melting point, i.e., a non solid state-oriented film.
The multilayer film can have desirable seal properties, e.g., a first component to second component seal strength of at least 4 pounds/inch at a seal time of 1.5 seconds on a VERTROD(copyright) impulse heat sealing machine with wires top and bottom, 70% seal power, total dwell time 5.0 seconds, and room temperature cooling, as well as a first component to second component seal strength of at least 6 pounds/inch at a seal time of 2.0 seconds on a VERTROD(copyright) impulse heat sealing machine with wires top and bottom, 70% seal power, total dwell time 5.0 seconds, and room temperature cooling. Second component to second component seal strength can be at least 8 pounds/inch at a seal time of 1.5 seconds on a VERTROD(copyright) impulse heat sealing machine with wires top and bottom, 70% seal power, total dwell time 5.0 seconds, and room temperature cooling.
The multilayer film of the invention can have at least one of its film layers comprising pigment. The second component can have an outside surface which contains no added antiblock additive and no added slip additive. The resulting film has adequate machinability in the absence of such additives as well as enhanced stackability of product due to increased coefficient of friction (COF). The second component is preferably no greater than 1.5 mil thick.
The first component can comprise a crosslinked polymer network. Preferably, the crosslinked polymer network is produced by irradiation, preferably irradiation at a level of from about 0.5 to 15 MR (i.e., 5 to 150 kGy); more preferably, from about 1 to 8 MR (i.e., 10-80 kGy), still more preferably, from about 3 to 5 MR (i.e., 30-50 kGy).
The multilayer film can have a tear propagation of 100 to 300 grams, an outside surface having a gloss of at least 70 percent, a static COF of at least 0.6 and a kinetic COF of at least 0.5, as measured between outer fourth film layer surfaces, i.e., the surfaces involved in package to package contact during stacking of bags.
The multilayer film can comprise trap printing between the third layer and the fourth layer.
In another aspect, the present invention relates to a sealed article comprising a two-component laminated multilayer film which comprises:
I. a first component comprising:
(A) a first film layer which is an inside film layer comprising ethylene/alpha-olefin copolymer;
(B) an optional second film layer comprising at least one member selected from the group consisting of ethylene/unsaturated ester copolymer, anhydride-modified ethylene/alpha-olefin copolymer, anhydride-modified ethylene/ester copolymer, acid-modified ethylene/alpha-olefin copolymer, and acid-modified ethylene/acid copolymer;
(C) an optional third film layer comprising ethylene/alpha-olefin copolymer; and
II a non heat-shrinkable second component laminated to said first component, said second component comprising:
(D) a fourth film layer which comprises at least one member selected from the group consisting of ethylene/alpha-olefin copolymer and ethylene/unsaturated ester copolymer;
(E) a fifth film layer which serves as an O2-barrier layer, the fifth film layer being between the third film layer and the fourth film layer, the fifth film layer comprising at least one member selected from the group consisting of PVDC, EVOH, polyalkylene carbonate, polyacrylonitrile, polyamide, and polyester;
(F) a sixth film layer which is between the fourth film layer and the fifth film layer, the sixth film layer serving as a first tie layer and comprising at least one member selected from the group consisting of ethylene/unsaturated ester copolymer, anhydride-modified ethylene/alpha-olefin copolymer, anhydride-modified ethylene/ester copolymer, acid-modified ethylene/alpha-olefin copolymer, and acid-modified ethylene/acid copolymer; and
(G) a seventh film layer which is between the third film layer and the fifth film layer, the seventh film layer serving as a second tie layer and comprising at least one member selected from the group consisting of ethylene/unsaturated ester copolymer, anhydride-modified ethylene/alpha-olefin copolymer; anhydride-modified ethylene/ester copolymer, acid-modified ethylene/alpha-olefin copolymer, and acid-modified ethylene/acid copolymer;
wherein the article comprises a seal of the film to at least one member selected from the group consisting of itself and another film, and a surface of said second component is heat sealable to itself as well as to said inside layer (A) of said first component.
Preferably, the article comprises a bag. Although the bag is preferably a gusseted bag, which can have side gussets or a bottom gusset, the bag can also be a non-gusseted end-seal bag or a non-gusseted side seal bag.
In a third embodiment, the present invention relates to a packaged product comprising a two-component laminated multilayer film which comprises:
I. a first component comprising:
(A) a first film layer which is an inside film layer comprising ethylene/alpha-olefin copolymer;
(B) an optional second film layer comprising at least one member selected from the group consisting of ethylene/unsaturated ester copolymer, anhydride-modified ethylene/alpha-olefin copolymer, anhydride-modified ethylene/ester copolymer, acid-modified ethylene/alpha-olefin copolymer, and acid-modified ethylene/acid copolymer;
(C) an optional third film layer comprising ethylene/alpha-olefin copolymer; and
II. a non heat-shrinkable second component laminated to said first component, said second component comprising:
(D) a fourth film layer which comprises at least one member selected from the group consisting of ethylene/alpha-olefin copolymer and ethylene/unsaturated ester copolymer;
(E) a fifth film layer which serves as an O2-barrier layer, the fifth film layer being between the third film layer and the fourth film layer, the fifth film layer comprising at least one member selected from the group consisting of PVDC, EVOH, polyalkylene carbonate, polyacrylonitrile, polyamide, and polyester;
(F) a sixth film layer which is between the fourth film layer and the fifth film layer, the sixth film layer serving as a first tie layer and comprising at least one member selected from the group consisting of ethylene/unsaturated ester copolymer, anhydride-modified ethylene/alpha-olefin copolymer, anhydride-modified ethylene/ester copolymer, acid-modified ethylene/alpha-olefin copolymer, and acid-modified ethylene/acid copolymer; and
(G) a seventh film layer which is between the third film layer and the fifth film layer, the seventh film layer serving as a second tie layer and comprising at least one member selected from the group consisting of ethylene/unsaturated ester copolymer, anhydride-modified ethylene/alpha-olefin copolymer, anhydride-modified ethylene/ester copolymer, acid-modified ethylene/alpha-olefin copolymer, and acid-modified ethylene/acid copolymer,
wherein the packaged product comprises a seal of the film to at least one member selected from the group consisting of itself and another film, and a surface of said second component is heat sealable to itself as well as to said inside layer (A) of said first component.
The package comprises the article in accordance with the present invention, preferably a preferred article according to the present invention. The article serves as a package which surrounds a packaged product which comprises hard, flowable, particulates, and/or a non-flowable product comprising cheese. Preferably, the hard, flowable particulates comprise food. Preferably, the food product comprises at least one member selected from the group consisting of pet food, livestock feed, sugar, coffee, cookies, cereal, cake mix, crackers, chips, powdered milk, and plant food. Other hard, flowable products include charcoal, cement, fertilizer, lime, pesticide, and herbicide.
At least one film layer can comprise pigment. The article can also have trap printing between the third layer and the fourth layer. Alternatively, printing can be present on an outside surface of the second outer layer.